The apparatus described herein is a closure system particularly adapted to use in conjunction with pilings which are driven through piling guides to secure an offshore drilling platform to the ocean floor.
Offshore drilling platforms are generally supported by towers constructed of prefabricated sections secured thereto. The offshore drilling platform support structure generally comprises a base which is anchored by pilings to the ocean floor. A typical support structure has a plurality of main legs sections and if employed as a base section which is to be anchored to the ocean floor, the section will be supplied with piling guides comprising pipe having an outside diameter of, for example, six to seven feet or less. The pilings have an equal diameter and are slideably disposed through the piling guides. Pilings are driven through a rupturable seal assembly secured on the lower end of the piling guides such as that disclosed in U.S. Pat. No. 3,533,241 to Bowerman, et al, entitled "Rupturable Seal Assembly for Piling Guides".
The pilings are generally separate from the base of the offshore drilling platform and are generally floated to the site for positioning in the piling guides after the base has been flooded and positioned on the ocean floor. The pilings usually have an upper and lower closure for sealing off the pile and preventing hydrostatic pressure from entering the pile. The pilings must be flooded and guided downwardly prior to engaging the piling guide and being driven in position and exposed to hydrostatic pressures in an excess of 650 psi. It is desirable to provide controlled flooding of the pile or other tubular member to allow more accurate positioning of the piling within the piling guide, and to prevent rupture of the piling which is usually several hundred feet long and very flexible.
The tube closure may also be employed in piling guides and main legs of the support structure to allow the structure to be set gently on the ocean floor.
Heretofore, pipe closure plugs have been employed to control the flooding. Typical pipe closure systems are disclosed in the following U.S. Pat. Nos.: 3,537,483; 3,593,749; 3,724,273; 3,746,026; 3,884,261; and 3,943,982. These devices generally relate to retractable plugs used in pipe lines having a much smaller diameter than pilings. Generally, as disclosed in U.S. Pat. No. 3,537,483 the devices require a flange which is not possible to provide with the seamless exterior wall of the piling which must be driven through a piling guide. Some devices disclosed in the patents listed above rely on frictional forces with the interior wall of the pipe which would not be sufficient to withstand the extreme hydrostatic pressures encountered in installation of offshore drilling platforms.
The devices generally disclose long linkage arms to retract the locking mechanism which is not practical when used in the pilings.